Internal combustion engines supplying motive power to a vehicle generate power not only for propulsion, but also to operate various systems associated with the engine. For example, a fuel pump can be mechanically driven from a power take-off on the engine, or can be electrically driven from a battery that is supplied electrical power from an alternator driven by the engine. In both circumstances, the engine provides power to drive the fuel pump. Over the range of engine operating conditions the engine supplies sufficient power to the fuel pump to meet the fuel demand of the engine.
In all applications there is a finite source of power available from the engine for subsystems to operate without significantly affecting engine efficiency. Continuous improvement in these subsystems reduces power consumption and improves their performance. In high horse power applications the amount energy generated by the engine is relatively large and the power requirement for engines subsystems to operate is significant. Stringent power budgets are established for specific engine components such that the overall system performance can be successfully managed. One such application is in the rail industry, where one or more locomotives supply electrical power to drive a liquefied gaseous fuel pumping apparatus on a tender car. Each locomotive comprises an internal combustion engine that is fuelled with a gaseous fuel stored in liquefied form for driving electrical generators that generate alternating current (AC) or direct current (DC) electrical energy employed to power electric traction motors in the propulsion system as well as to power other subsystems. One of these electrical generators is known as a companion-alternator that supplies AC electrical energy to components such as cooling fans, cooling pumps, cabin heaters and coffee makers, and to the tender car for the purpose of operating the liquefied gaseous fuel pumping apparatus.
In addition to operating in idle, the locomotives operate in modes called notches, for which conventionally there are 8 levels respectively named Notch 1 up to Notch 8. Each higher notch level represents a higher engine load/speed operating point, and consequently a higher fuel demand. For each subsequently higher notch level, the nature of the AC electrical energy generated by the locomotive changes in both voltage and frequency, since the generators are directly driven by the crank-shaft of the locomotive engine, and as the engine speed varies the generator output varies. Additionally, the amount of AC electrical power that the locomotive can supply increases for each higher notch level since the companion-alternator energy output is directly related to engine speed. A further operating mode, called dynamic braking, occurs when the locomotive is going downhill, where the electric generator is used to slow the train down, and the energy generated is run through large resistor banks on the locomotive.
For each notch level there is a maximum instantaneous electrical power available from the locomotive that the fuel pumping apparatus can consume such that the locomotive can operate at a predetermined performance and efficiency. When the liquefied gaseous fuel pumping apparatus consumes more than the maximum available electrical power, other subsystems may be starved of energy. The maximum instantaneous electrical power is both a maximum-continuous and maximum-peak power level.
The liquefied gaseous fuel pumping apparatus comprises a cryogenic pump that pressurizes the liquefied gaseous fuel upstream of a heat exchanger for vaporizing the gaseous fuel for delivery to a fuel injection system on the locomotive engine. Cryogenic pumps can be reciprocating piston-type pumps that comprise a hydraulic motor and a pump. Unlike fuel pumps associated with conventional liquid fuels such as diesel, cryogenic pumps are operated under extreme environmental conditions that result in unique design requirements that tend to increase the size and power consumption of these pumps compared to diesel fuel pumps. When the gaseous fuel is directly injected into cylinders in the locomotive engine late in the compression cycle, the gaseous fuel pressure must be high enough to overcome the cylinder pressure at the time of injection. The cryogenic pump consumes more power as the gaseous fuel pressure downstream from the pump increases. Even though there is a challenge in designing a liquefied gaseous pumping apparatus for supplying high pressure gaseous fuel suitable for direction injection in a locomotive engine, the benefits of increased power and torque and reduced emissions are worth the costs associated therewith.
A gaseous fuel is any fuel that is in a gas state at standard temperature and pressure, which in the context of this application is 20 degrees Celsius (° C.) and 1 atmosphere (atm). An exemplary gaseous fuel is natural gas, which when stored in a liquefied form at cryogenic temperatures is referred to as liquefied natural gas (LNG). Other examples of gaseous fuels include butane, ethane, hydrogen, propane, and mixtures thereof, and as would be known to one skilled in the art there are many other such examples. Normally, LNG is stored in a vacuum insulated storage vessel at or near its boiling point, which is approximately −160° C. A cryogenic temperature is any temperature typically below −150° C.
There is a need for a gaseous fuel system that can meet the fuel demand of high horse power engines, such as locomotive engines, without consuming more than the maximum instantaneous electrical power at the specified notch level. The state of the art is lacking in techniques for supplying an internal combustion engine with gaseous fuel stored in liquefied form. The present method and apparatus provides a technique for improving a liquefied gaseous fuel pumping system for internal combustion engines.